Engine control apparatus

ABSTRACT

An engine control apparatus is provided with a control unit in which a fuel supply quantity Q f  or a ignition timing θ i  is corrected to maximize an evaluation parameter A=P i  /(Q a  /N) obtained on the basis of a suction air quantity Q a , an engine speed N and a mean effective pressure P i  in a engine, or to maximize a parameter B=P i  /P b  obtained on the basis of a suction pipe pressure P b  and the mean effective pressure P i , or to maximize a maximum pressure P max  or a mean effective pressure P i  for every combustion cycle, so that control is performed on the basis of the result of the above correction. The control unit also performs the feedback control of the fuel supply quantity Q f  and corrects the ignition timing by the above-mentioned correction means. Further, the control unit performs feedback control in a predetermined load-operation range of the engine, and stops the feedback control and corrects the fuel supply quantity Q f  out of said predetermined load-operation range of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine controlapparatus in which maximum power and maximum efficiency can be obtainedin spite of scatter in performance of engines.

2. Prior Art

Heretofore, there has been used an apparatus for controlling a fuelinjection valve and an ignition device by calculating a proper fuelsupply quantity and ignition timing on the basis of the relationshipbetween a suction air quantity or suction pipe pressure and an enginespeed (rpm).

Further, a control apparatus designed to perform higher-precisioncontrol by detecting the combustion pressure of the engine and adjustingthe pressure to a predetermined value has been disclosed in JapanesePat. Unexamination Publication No. 62-85148.

In this control apparatus, the combustion condition is detected by theoutput of a cylinder internal pressure (combustion pressure) sensorprovided in every cylinder so that the controlling of combustioninjection timing, EGR (exhaust gas recycle) valves and the like arecarried out to fit the condition in a predetermined pattern.

In the aforementioned prior art apparatus, control is carried out to fitthe combustion pressure to a combustion pattern determined in advance bya standard engine. In the case where a large number of engines aremass-produced, there arises considerable scatter. Accordingly,individual engines require individually different combustion patterns.For this reason, it cannot be absolutely said that precision incontrolling is improved by controlling the combustion pressure by use ofa uniform standard pattern. On the contrary, the performance of theengine may be rather lowered by such control.

Further, in the prior art apparatus, the fuel injection timing, the EGRrate and the like are controlled as operation parameters for controllingthe combustion pressure. However, the most effective parameters for theoutput performance of the engine are the combustion injection quantityand ignition timing optimum thereto.

In general, the freely controllable range of the fuel injection quantityis limited for the purpose of suppressing the component concentration ofthe exhaust gas to a low level. Accordingly, it is necessary to controlthe fuel injection quantity and the ignition timing comprehensively toreconcile the components of the exhaust gas and the power performance ofthe engine.

Further, in a gasoline engine, in order to clean up exhaust gas andimprove the output power of the engine, it is necessary to properlycontrol the air-fuel ratio and ignition timing in accordance with theoperating condition of the engine. Therefore, a method using amicro-computer to control the air-fuel ratio and ignition timing hasbeen widely used in the field of car gasoline engine.

For example, the air-fuel ratio control based on the quantity of fuelinjection is carried out in such a manner as follows. The quantity ofsuction air (Q_(a)) in the engine is detected by an air-flow sensorprovided in an air-intake passage. The engine speed or the number ofengine revolutions per unit time (N_(e)) is obtained from the output ofa rotation sensor provided on a crankshaft or the like. The quantity ofair per engine revolution (Q_(a) /N_(e)) is calculated and, accordingly,the quantity of basic fuel injection is calculated based on the quantityof air (Q_(a) /N_(e)). The quantity of basic fuel injection is used forthe purpose of obtaining a target air-fuel ratio at every predeterminedoperation point. Then, a correction is carried out in accordance withthe output of a water sensor or the like provided to detect thetemperature of engine cooling water to thereby finally decide thequantity of fuel injection. On the basis of an injection pulse signalhaving a pulse width corresponding to the thus decided fuel injectionquantity, an injector is actuated to open its valve in synchronism withthe rotation of the engine to inject fuel into, the engine. Further, ina low and partial load range, an air-fuel ratio sensor in which theoutput thereof rapidly changes in the vicinity of the theoreticalair-fuel ratio is used to thereby judge whether the actual air-fuelratio is on a rich side or on a lean side. A feedback correction basedon the judgment is applied to the quantity of fuel injection so that theair-fuel ratio of the engine is controlled so as to be converged intothe theoretical air-fuel ratio. By controlling the air-fuel ratio to bealways the theoretical air-fuel ratio, cleaning of exhaust gas can becarried out with high efficiency by used of ternary catalystic method.

On the other hand, the control of ignition timing is carried out in sucha manner as follows. In general, an ignition timing advancepredetermined in the form of a map corresponding to the air quantity(Q_(a) /N_(e)) and the engine speed (N_(e)) is read. The currentconduction of an ignition coil is controlled by an ignition signal basedon the thus read-out ignition timing advance.

In general, the ignition timing advance is determined so as to aim atMBT (minimum ignition timing advance required for producing maximumengine torque). Because MBT varies widely according to several factors,such as scatter in engine temperature and air-fuel ration, dimensionalerror in the combustion chamber, temperature and humidity of suction airand the like, it is difficult to obtain optimum ignition timingcontinuously by such a simple "open" control method. There exists aproblem in that knocking trouble may occur or reduction of torque mayoccur. Therefore, such an improvement has been proposed as described inJapanese Pat. Unexamination Publication No. 62-82273. The improvement isconstructed so that the ignition timing feedback control is carried outon the basis of the measured value of cylinder internal pressure tomaximize the engine torque. According to the cylinder internal pressurefeedback control method, for example, a rotation sensor is provided togenerate a pulse for every degree (1° C.) of crank angle. The outputvalue (P₀) of the cylinder internal pressure sensor measured for everypulse generation is read successively, so that mean effective pressure(P₁ ) represented by the following equation is calculated from cylindervolume (V) and piston displacement (V_(n)) corresponding to thecurrently obtained crank angle. ##EQU1## Consequently, the ignitiontiming feedback control is carried out to maximize P₁.

As described above, the conventional cylinder internal pressure feedbackcontrolling method has an attempt to obtain maximum torque by correctingignition timing to maximize mean effective pressure (P₁). However, theair-fuel ratio feedback control is stopped in a high load range, so that"open" control is carried out in the high load range. Accordingly,air-fuel ratio error caused by scatter in characteristics of sensors,injectors and fuels is produced as reduction of torque. Accordingly, itis impossible to draw out the best in the torque of the engine even ifcylinder internal pressure feedback control is carried out by correctingignition timing.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an enginecontrol apparatus which is capable of controlling the combustioncondition of an engine suitably corresponding to the operation conditionof the engine and capable of drawing out maximum power and maximumefficiency to thereby solve the aforementioned problem.

It is another object of the present invention to provide an enginecontrol apparatus which is capable of drawing out the best in the torqueof the engine even in a high load range by a cylinder internal pressurefeedback control method to thereby solve the aforementioned problem.

The engine control apparatus according to the present invention isprovided with a control unit in which the fuel supply quantity Q_(f) orthe ignition timing θ_(i) is corrected so as to maximize the evaluationparameter A=P_(i) /(Q_(a) /N) obtained on the basis of the suction airquantity Q_(a), the engine speed N and the mean effective pressure P_(i)in the engine, or to maximize the parameter B=P_(i) /P_(b) obtained onthe basis of the suction pipe pressure P_(b) and the mean effectivepressure P_(i), or to maximize the maximum pressure P_(max) or meaneffective pressure at P_(i) at every combustion cycle, so that controlis performed on the basis of the result of the above correction.

Also, the internal combustion engine control apparatus according to theinvention is provided with a control unit which performs the feedbackcontrol of the fuel supply quantity Q_(f) and corrects the ignitiontiming by the above-mentioned correction means.

Further, the internal combustion engine control apparatus according tothe invention is provided with a control unit which performs feedbackcontrol in a predetermined load-operation range of the engine, and stopsthe feedback control and corrects the fuel supply quantity Q_(f) inother operation ranges of the engine.

Further, the engine control apparatus according to the present inventioncomprises: an air-fuel ratio control means for controlling the air-fuelratio of an engine; an ignition timing control means for controlling theignition timing of the engine; an air-fuel ratio detection means fordetecting the air-fuel ratio of the engine; a load detection means fordetecting the load of the engine; a cylinder internal pressure detectionmeans for detecting the internal pressure of a cylinder of the engine; afirst cylinder internal pressure feedback control signal generationmeans responsive to the output of the cylinder internal pressuredetection means for generating a first cylinder internal pressurefeedback control signal and for applying the first cylinder internalpressure feedback control signal to the ignition timing control means tothereby substantially maximize the output torque of the engine on thebasis of the cylinder internal pressure; a load judgment meansresponsive to the output of the load detection means for judging whetherthe load of the engine is in a low or partial load range or in a highload range; an air-fuel ratio feedback control signal generation meansfor generating an air fuel ratio feedback control signal and forapplying the air-fuel ratio feedback control signal to the air-fuelratio control means to thereby converge the air-fuel ratio to atheoretical value when the load judgment means proves that the load ofthe engine is in the low or partial load range; and a second cylinderinternal pressure feedback control signal generation means forgenerating a second cylinder internal pressure feedback control signaland for applying the second cylinder internal pressure feedback controlsignal to the air-fuel ratio control means to thereby substantiallymaximize the torque of the engine when the load judgment means provesthat the load of the engine is in the high load range. The apparatus hasa feature particularly in that the air-fuel ratio feedback control aswell as the ignition timing feedback control is carried out tosubstantially maximize the torque of the engine in a high load range inwhich the air-fuel ratio feedback control has not been carried out inthe prior art.

The control apparatus according to the present invention obtains themaximum pressure P_(max) or the mean effective pressure P_(i) for everycombustion cycle on the basis of the combustion chamber pressure P_(c)and the crank angle θ_(c), corrects the fuel supply quantity Q_(f) orthe ignition timing θ_(i) to maximize at least one of the maximumpressure P_(max), the mean effective pressure P_(i) and the evaluationparameters A and B, and supplies fuel to the engine on the basis of thecorrected fuel supply quantity Q_(f) or performs ignition control basedon the corrected ignition timing θ_(i).

Also, the control apparatus according to the invention detects theair-fuel ratio based on the component concentration of a combustion gasdetected by the exhaust sensor, performs the feedback control of thefuel supply quantity Q_(f) to make the air-fuel ratio be a predeterminedvalue, and corrects the ignition timing θ_(i) to maximize at least oneof the maximum pressure P_(max), the mean effective pressure P_(i) andthe evaluation parameters A and B.

Further, the control apparatus according to the invention detects theair fuel ratio based on the component concentration of a combustion gasdetected by the exhaust sensor, perform the feedback control of the fuelsupply quantity Q_(f) to make the air-fuel ratio be a predeterminedvalue, and stops the feedback control in a predetermined load-operationrange of the engine and, at the same time, corrects the fuel supplyquantity Q_(f) to maximize at least one of the maximum pressure P_(max),the mean effective pressure P_(i) and the evaluation parameters A and B.

Further, in a low or partial load range, the air-fuel ratio feedbackcontrol means is operated to carry out the air fuel ratio feedbackcontrol based on the output of the air-fuel ratio detection means. Asthis result, the air-fuel ratio of the engine is substantially convergedinto a theoretical air-fuel ratio. Further, the ignition timing feedbackcontrol is carried out based on the output of the cylinder internalpressure detection means to substantially maximize the torque of theengine.

In a high load range, both the ignition timing feedback control and theair-fuel ratio feedback control are carried out based on the output ofthe cylinder internal pressure detection means. As a result, theinternal pressure (combustion pressure) of the cylinder is controlled sothat maximum torque can be obtained under the condition that theair-fuel ratio is rich.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the internal combustion engine control apparatusas one embodiment of the present invention;

FIG. 2 is a block diagram showing the internal construction of thecontrol unit in the embodiment of FIG. 1;

FIG. 3 is a characteristic graph showing an example of the combustionpressure waveform in the embodiment of FIG. 1;

FIGS. 4 and 5 are characteristic graphs showing the relationshipsbetween the combustion parameters, the air-fuel ratio and the ignitiontiming, respectively;

FIGS. 6(a) through 6(c), 7 and 8 are flow charts showing the flow of theoperation for performing the maximum value control according to thepresent invention, respectively;

FIG. 9 is an explanatory view showing an example of the zone separationof the operation condition and the assignment of the memories;

FIG. 10 is a flow chart showing the flow of the operation in a transientstate according to the present invention;

FIG. 11 is a diagram showing the whole configuration of the enginecontrol apparatus according to another embodiment of the presentinvention;

FIG. 12 is a partly block diagram showing the embodiment;

FIGS. 13 through 15 are characteristic graphs for explaining thecontrolling operation of the embodiment, respectively; and

FIG. 16 is a flow chart for execution of the controlling operation ofthe embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the drawings. FIG. 1 is a diagram showing the mainconstruction of an embodiment of the present invention. In the drawingthe reference numeral 1 designates an air cleaner; 2, an air-flow meterfor measuring the quantity of suction air; 3, a throttle valve; 4, asuction air manifold; 5, a cylinder block; 6, a water temperature sensorfor detecting the temperature of engine cooling water; and 7, a crankangle sensor.

The crank angle sensor 7 generates a reference position pulse at everyreference position of the crank angle (for example, for every 180degrees in a 4-cylinder engine or for every 120 degrees in a 6-cylinderengine) and generates a unit angle pulse for every unit angle (forexample, for every 1 degree).

The reference numeral 8 designates an exhaust manifold; 9, an exhaustsensor for detecting the component concentration (for example, oxygenconcentration) of an exhaust gas; 10, a fuel injection valve; 11, anignition plug, 13 a cylinder internal pressure sensor (hereinafterreferred to as "combustion pressure sensor") for detecting the internalpressure of the cylinder; and 15, a control unit.

In the control unit 15, the instantaneous crank angle can be known bycounting the number of unit angle pulses after the input of a referenceposition pulse.

Further, the engine speed can be known by measuring the frequency orcycle of the unit angle pulses.

Although the embodiment of FIG. 1 has shown the case where the crankangle sensor is provided in a distributor, the invention is applicableto the case where the crank angle sensor is directly connected to acrankshaft.

The reference numeral 2a designates a suction pipe pressure sensor. Anyone of the output of the sensor 2a and the output of the air-flow meter2 is used for the feedback control of the fuel supply quantity and theignition timing.

The control unit 15 has the construction as shown in FIG. 2. In thedrawing, the reference numeral 151 designates an A/D (analog-to-digital)converter which receives the output S1 of the air-flow meter 2 or theoutput S1a of the suction pipe pressure sensor 2a, the output S2 of thewater temperature sensor 6, the output S4 of the exhaust sensor 9, andthe output S6 of the combustion pressure sensor 13.

The reference numeral 152 designates and input interface which receivesthe output S3 of the crank angle sensor 7.

The reference numeral 153 designates a CPU which operates together withan ROM 154 and an RAM 155 to process the aforementioned input signal inaccordance with a predetermined program.

The reference numeral 156 designates an output interface which receivesthe output of the CPU 153 and produces its output signals S5 and S6. Theoutput S5 is a pulse signal for actuating the fuel injection valve 10.The fuel supply quantity can be controlled by the pulse width of thepulse signal.

The output S7 is an ignition timing signal which is amplified by a powerunit 16. The ignition coil 17 is operated by the output S8 of the powerunit 16.

The output S9 of the ignition coil 17 is distributed as an output S10,by the distributor 18, into the ignition plugs 11 respectively providedin the cylinders.

In the following, the operation is described. The basic method forcontrolling the fuel injection and the ignition timing based on theoutput of the air-flow meter 2 or the suction pipe pressure sensor 2a inthe apparatus of FIG. 1 is well known, and the detailed descriptionthereof will be omitted. The operation related to the present inventionwill be therefore described in detail.

Referring to FIG. 3, the relation between the combustion pressure P_(c)and the crank angle θ_(c) is shown. In FIG. 3, the output S6 of thecombustion pressure sensor 13 takes a maximum value in the vicinity of acrank angle upper dead point (TDC). Let the maximum value be P_(max).

Mean effective pressure P_(i) (cylinder internal pressure) is calculatedby integrating the combustion pressure P_(c) over one cycle as follows.##EQU2##

In the equation (1), V_(s) is the piston displacement represented by theequation: ##EQU3## Further, V is the cylinder volume and represented bythe following equation (2): ##EQU4## in which l is the control length, ris the piston stroke and θ_(c) is the crank angle.

Accordingly, the following equation (3) is obtained from the equation(2). ##EQU5##

Accordingly, the mean effective pressure P_(i) can be calculated bysubstituting the equation (3) into the equation (1).

The mean effective pressure P_(i) thus obtained is well known as aparameter for directly detecting the power output of the engine.

Other parameters A and B can be calculated from the mean effectivepressure P_(i), the suction air quantity Q_(a) of the engine obtainedbased on the output S1 of the air-flow meter 2 or the suction pipepressure P_(b) obtained based on the output S1a of the suction pipepressure sensor 2a, and the engine speed N obtained based on the crankangle. These parameters A and B are also useful as parameters forevaluating combustion energy or efficiency from the quantity (Q_(a) /Nor P_(b)) of suction air per stroke, of the engine.

    A=P.sub.i /(Q.sub.a /N)                                    (4)

    B=P.sub.i /P.sub.b                                         (5)

Typical relations between these evaluation parameters (P_(max), P_(i),A, B), air-fuel ratio and ignition timing are as shown in FIGS. 4 and 5.

As shown in FIG. 4, P_(max) and P_(i) have maximum values. It isapparent from FIG. 4 that the maximum output power can be obtained bycontrolling the air-fuel ratio to maximize these parameters.

Further, the evaluation parameters A and B are parameters for expressingcombustion energy which can be drawn out from the quantity of suctionair per stroke. It is known that optimum efficiency can be obtained bycontrolling the air-fuel ratio to maximize the parameters A and B.

As shown in FIG. 5, P_(max) increases as the ignition timing θ_(ig) isadvanced, but the mean effective pressure P_(i) and the evaluationparameters A and B have maximum values.

In the engine having such performance, the maximum power and optimumefficiency can be obtained by controlling the ignition timing tomaximize the mean effective pressure P_(i) and the evaluation parametersA and B.

The aforementioned controlling operation will be described more indetail with reference to the flow charts of FIGS. 6(a) and 6(b).Referring now to FIG. 6(a), there is shown a flow chart for detectingcombustion pressure. In the step 101, the output θ_(c) of the crankangle sensor is read out. The output of the crank angle sensor may beproduced by counting pulses generated for every predetermined degree(for example, 1° ) of crank angle or may be produced in the form of acode corresponding to the angle.

Then, in the step 102, the output P_(c) of the combustion pressuresensor 13 is read out. The reading of P_(c) is carried out for everypredetermined degree (for example, 1° ) of crank angle.

Then, in the step 103, a judgment is made as to whether P_(c) is largerthan P'_(max) or not. Because P'_(max) is cleared up in an initial stageof one cycle of combustion, the first read value of P_(c) is larger thanP'_(max). Accordingly, in the step 104, P_(c) is kept at P'_(max).

Then, in the step 105, the mean effective pressure P'_(i) is calculatedby the aforementioned equation. Then, in the step 106, a judgment by thevalue of crank angle signal θ_(c) is made as to whether one cycle ofcombustion is terminated or not. When not terminated, the step isreturned to the step 101.

As described above, P'_(max) is successively updated to a larger valueby the step 104 when P_(c) increases. When P_(c) decreases, theprocedure of the step 104 is omitted so that the maximum value of P_(c)in one combustion cycle can be kept at P'_(max).

At the point of time one cycle is terminated, the step is shifted fromthe step 106 to the step 107. In the step 107, P'_(max) is stored inP_(max). Then, in the step 108 p'_(i) is stored in P_(i). Then, in thestep 109, P'_(max) and P'_(i) are cleared up. Thereafter, theaforementioned procedure from the step 101 is repeated for a new cycle.

The aforementioned values of P_(max) and P_(i) are used in the followingfuel control and ignition timing.

FIG. 6(b) is a flow chart for controlling the fuel injection quantity tomaximize the mean effective pressure P_(i) obtained by the procedure ofFIG. 6(a). Though not shown, the initial values P_(i)(0) and P_(i)(1) ofthe mean effective pressure P_(i) are set to be zero.

In FIG. 6(b), the step 201 is provided for reading mean effectivepressure P_(i) held in a (n-1)th combustion cycle, that is to say, thereading P_(i)(n-1). Similarly, the step 202 is provided for reading meaneffective pressure P_(i) held in a (n)th combustion cycle, that is tosay, for reading P_(i)(n).

Then, in the step 203, the sizes of P_(i)(n) and P_(i)(n-1) arediscriminated. Because P_(i)(1) is equal to P_(i)(0) in the initialstage, the step is shifted to the step 204. In the drawing, T_(n)represents a pulse width by which the fuel injection valve was operatedat the last time. In the initial stage, T_(n) is set to be a pulse widthT₀. This pulse width T₀ corresponds to the reference air-fuel ratio(A/F)₀ in FIG. 4. A pulse width T₁ for the next combustion cycle isobtained by subtracting ΔT from the pulse width T₀.

Then, in the step 206, the fuel injection valve is operated by the pulsewidth T₁. Because the pulse width T₁ is less than the pulse width T₀ byΔT, the air-fuel ratio is shifted to a lean side in FIG. 4 so that themean effective pressure P_(i)(2) produced by this injection becomeslarger than P_(i)(1).

This mean effective pressure P_(i)(2) is read out in the step 207. Inthe step 208, the mean effective pressure P_(i)(0) is replaced byP_(i)(1). In the step 209, the mean effective pressure P_(i)(1) isreplaced by P_(i)(2). Further, in the step 210, the pulse width T₀ isreplaced by T₁. Thereafter, the step is returned to the step 201.

As described above, the pulse width T_(n+1) is reduced whenever Δ issubtracted by the step 204. Consequently T_(n+1) approaches the pulsewidth T_(opt) corresponding to the optimum air-fuel ratio (A/F)_(opt) asshown in FIG. 4.

When T_(n+1) is further reduced to be smaller than the pulse widthT_(opt), the mean effective pressure P_(i) is reduced reversely.

Because the relation P_(i)(n) <P_(i)(n-1) is established in the step203, the step is shifted to the step 205. In the step 205, the pulsewidth T_(n+1) is reversely set to be larger than the last value T_(n) byΔT.

When the aforementioned operation is repeated, the pulse width T_(n+1)is converged in the vicinity Of T_(opt) so that the mean effectivepressure P_(i) is adjusted to be in the vicinity of its maximum value.The subtrahend ΔT is established to be as small as possible. The reasonis in that the pulse width T_(n+1) changes widely in the vicinity ofT_(opt) as the subtrahend ΔT increases, to thereby make stable drivingin a value sufficiently near T_(opt) impossible.

FIG. 6(b) is a drawing simplified for the purpose of explaining theprinciple of operation. For this reason, the following operation errormay occur.

Assuming now that the pulse width T_(n) is between T₀ and T_(opt), thenthe pulse width T_(n) can be converged into T_(opt) by the subtractionshown in the step 204. However, if the addition in the step 205 ismistaken for the subtraction in the step 204, the mean effectivepressure P_(i) decreases and, accordingly, the addition in the step 205is carried out based on the judgment of the step 203 in the next cycle.Consequently, the pulse width will diverge toward the pulse width T₀.The aforementioned problem can be solved logically as shown in FIG.6(c).

FIG. 6(c) shows the point of improvement. Other portions not shown inFIG. 6(c) are the same as those in FIG. 6(b). In FIG. 6(c), the step 303is provided for setting the flip-flop I to be 0 when the subtraction iscarried out in the step 204. Similarly, the step 304 is provided forsetting the flip-flop I to be 1 when the addition is carried out in thestep 205. After the procedure of the step 304 or 303, the step isshifted to the step 206.

In the next cycle, the value of the flip-flop I is judged by the steps301 and 302 after the judgment of the step 203. If the flip-flop I hasbeen set to be 0 when the step is shifted from the step 203 to the step203, the mean effective pressure P_(i) has increased as the result ofthe subtraction. Accordingly, in this case, the subtraction in the step204 is carried out again to approach the pulse width T_(n+1) to T_(opt).

If the flip-flop I has been set to be 1, the mean effective pressureP_(i) has increased as the result of the last addition. Accordingly, adecision that the pulse width is on the right side of T_(opt) (that is,T_(n+1) <T_(opt)) is made. Accordingly, the step is shifted to the step205, so that the addition in the step 205 is carried out to approach thepulse width T_(n+1) to T_(opt). The operation in the step 302 is thesame as described above.

It is apparent from the above description that the flip-flop I isprovided for making a judgment as to whether the pulse width T_(n+1) ison the right side of T_(opt) or not to thereby prevent the pulse widthfrom diverging in the reverse direction as stated preliminarily.

Of course, in the initial stage, the flip-flop I must be set to be 0 aswell as the pulse width is set to be T₀.

The method for controlling the mean effective pressure P_(i) bycontrolling the fuel supply quantity has been described with referenceto FIGS. 6(a) through 6(c). The method for controlling the meaneffective pressure P_(i) by the ignition timing θ_(ig) will beunderstood easily when the pulse width T shown in the drawings isreplaced by the ignition timing θ_(ig). Accordingly, the detaileddescription thereof will be omitted.

Similarly, the control method for maximizing the maximum combustionpressure P_(max) and the evaluation parameters A=P_(i) /(Q_(a) /N),B=P_(i) /P_(b) will be understood easily when the mean effectivepressure P_(i) shown in the drawings is replaced by these parameters.Accordingly, the detailed description thereof will be omitted.

In the following, another embodiment of the present invention in whichthe aforementioned control method is practically applied is described.FIG. 7 shows an example of the maximum value control according to thepresent invention in the apparatus for performing feedback control so asto make the air-fuel ratio be a predetermined value by use of theexhaust sensor.

In the drawing, the step 401 is provided for making a judgment as towhether the air-fuel ratio feedback control based on the exhaust sensorcan be executed or not. The judgment is made from the operationcondition of the engine, the breakdown of the exhaust sensor and thelike.

In the case where this control is executed, the step is shifted to thestep 402. In the step 402, the output of the exhaust sensor 9 is readout. Then, in the step 403, the fuel supply quantity feedback control iscarried out to adjust the output of the exhaust sensor to apredetermined value. The controlling procedure is known commonly and thedetailed description thereof will be omitted.

Then, in the step 404, the ignition timing θ_(ig) is controlled tomaximize at least one of the evaluation parameters P_(max), P_(i), A andB. The control procedure is carried out by the maximum value control asexplained above with reference to FIGS. 6(a) through 6(c).

Then, the step is shifted to the step 405, when a decision that theair-fuel ratio feedback control is not executed is made in the step 401.In the step 405 the fuel supply quantity Q_(f) is controlled to maximizeat least one of the evaluation parameters P_(max), P_(i), A and B. Thiscontrol operation has been described with reference to FIGS. 6(a)through 6(c).

Then, the ignition timing θ_(ig) is controlled by the procedure of thestep 404. The flow chart of FIG. 7 is constructed so that the maximumvalue control based on the fuel supply quantity Q_(f) is not executedwhile the air-fuel ratio feedback control is executed. In short thecomponent concentration of an exhaust gas is kept in a predeterminedlevel or less, so that the air fuel ratio is controlled preferentially.

FIG. 8 shows a method for averaging the evaluation parameters used inthe aforementioned control. In the drawing, the step 501 is provided forreading the parameter X_(i) (which is the value of P_(max), P_(i), A orB in an (i)th cycle of combustion and corresponds to the output of thestep 107 or 108 in FIG. 6(a)). In the step 502, the parameter X_(i) isintegrated successively.

The step 503 is provided for making a judgment as to whether the numberof integrating operations has reached n (cycles) or not. If the numberhas not reached n, the step is shifted to the step 504 in which theaverage value X is obtained by dividing the integrated value by n. Thecontrol in FIGS. 6(b), 6(c) and 7 is carried out by the average value X.The averaging is made in consideration of the case where the combustionpressure P_(c) or the evaluation parameter P_(max), P_(i), A or Bchanges slightly to thereby interfere with the maximum value controlthough the engine is operated in the same fuel supply quantity Q_(f) andin the same ignition timing θ_(ig).

Considering the fact that learning speed becomes slower because of theaveraging, it is necessary to determine n within a range allowable forthe control. After the averaging, the integrated value is cleared up inthe step 505.

Although FIG. 8 shows a simple arithmetic averaging method, other knownmethods such as a weighted averaging method and a moving averagingmethod can be used.

In the maximum value control as explained above, it is desired that thecontrollable range related to the ignition timing control and the fuelsupply quantity control is limited. The reason is that lagging ignitiontiming causes an accidental fire or injury due to overheating of anexhaust gas and, on the contrary, leading ignition timing causeslowering of output power or injury due to abnormal combustion. In thecase where the fuel supply quantity is too much or in the case where thefuel supply quantity is too little, the same trouble occurs.

The limitation can be realized by controlling the ignition timing θ_(ig)and the fuel injection pulse width by upper and lower limits when theyare beyond the upper and lower limits. The logic is simple anddescription with reference to the drawing will be omitted.

As described above with reference to FIG. 6(b), the addend or subtrahendΔT (or Δθ_(ig) in the case of ignition timing) used for every cycle mustbe established to be as small as possible.

However, the fact that the addend or subtrahend is small means that thepulse width (ignition timing) is converged into an optimum value slowly.Accordingly, the fact is unsuitable for the control of the engine inwhich the operating condition changes continuously.

To solve such a problem, the operating condition of the engine isseparated into zones by the operation parameter. The maximum valuecontrol by means of the injection pulse width T_(n) or the ignitiontiming θ_(ig)(n) is carried out for every zone. The results of thecontrol, that is, T_(n) and θ_(ig)(n) are stored in memories providedcorresponding to the zones. The memories may be capable of storing theresults continuously after the power supply is cut.

In this case, the correction of the control parameters T_(n) andθ_(ig)(n) can be started from the vicinity of the respective optimumvalues when the engine is restarted or when the engine operatingcondition is shifted from one to another. Accordingly, the rate ofconvergence can be improved so that preferable control can be made.

To realize this control, the RAM 155 in FIG. 2 can be provided as anonvolatile memory or the power supply for the RAM 155 can be backed upby a battery to keep the contents of the RAM 155.

FIG. 9 is a view showing an example of the zone separation of theoperation condition and the assignment of the memories. In the drawing,the abscissa expresses the engine speed N which is separated into N₁, N₂and N₃. The ordinate Y expresses parameter showing the load of theengine. The suction air quantity Q_(a), the value Q_(a) /N obtained bydividing the suction air quantity Q_(a) by the engine speed N, suctionpipe pressure P_(b) and the like are used as the parameter. The ordinateY is similarly separated into Y₁, Y₂, Y₃ and Y₄.

Zone separation is carried out by N and Y so that memories M_(T) l,_(m)and Mθl,_(m) are assigned corresponding to the respective zones. In FIG.9, M_(T) represents a memory for keeping the control parameter T_(n) ,Mθ represents a memory for keeping the control parameter θ_(ig)(n), andl and m represent separation numbers in the abscissa and the ordinate,respectively.

In the case where the operation condition is in these zones, the maximumvalue control is carried out so that the control parameters aretemporarily written in the memories M_(T) and Mθ and kept therein.Although FIG. 9 shows the case where the operation condition isseparated into zones by two-dimensional parameters of the engine speed Nand the parameter Y showing the load of the engine, it is a matter ofcourse that the operation condition can be separated into zones by asingle parameter N or Y.

The logic of control in FIG. 9 is simple and the description thereofwith reference to the drawing will be omitted.

The control parameters stored in the memories M_(T) and Mθ can beconverted into proper values when the engine is stably operated in acorresponding zone.

In the case where acceleration and deceleration are repeated on theengine, however, the maximum value control may be carried outcorresponding to the transient state of combustion so that aberrantvalues may be stored in the memories.

To solve such a problem, a filter as shown in FIG. 10 can be used. InFIG. 10, the step 601 is provided for reading the pulse width T_(n) (thevalue of the step 210 in FIG. 6(b)) as one of the maximum value controlparameters. Then, in the step 602, the last value T_(o) (old) which hasbeen stored in the memory M_(T) is read. In the step 603, the followingarithmetic operation is carried out based on T_(n) and T_(o) (old).

    T.sub.o (new)=(1-K).T.sub.o (old)+KT.sub.n

In the arithmetic operation, K satisfies the relation 0<K≦1.

The meaning of this arithmetic operation is that a value T_(o) (new) tobe newly kept in the memory is produced so that K times the currentlyobtained result T_(n) is reflected in the memory. The value of K isdetermined by even balance between the suitable convergence speed of thevalue to be kept in the memory and the suppression of aberrantcorrection value in the transient state.

Then, in the step 604, the pulse width T_(o) (new) is written in thememory M_(T). Thereafter, the step is returned to the step 601. Thevalue T_(o) stored in the memory M_(T) is used as an initial value ofpulse width T_(n) when the maximum value control of FIG. 6(b) starts.

In FIG. 10, the steps 601 to 604 may be circulated in synchronism withthe maximum value control of FIG. 6(b) or may be circulated in a morelagging cycle.

Although FIG. 10 shows the case where the pulse width T_(n) is used asone of the control parameters, it is a matter of course that theignition timing θ_(ig)(n) can be stored in the memory M in the samemanner as described above.

The execution of the aforementioned maximum value control had betterstop when the operation of the combustion pressure sensor 13 isabnormal. Accordingly, a range of output value obtained from thecombustion pressure sensor 13 which is in a normal state had better bedetermined in advance so that a flag for inhibiting the maximum valuecontrol can be set when a value beyond the range is obtained from thecombustion pressure sensor 13. In short, the flag is read when themaximum value control starts, so that the control is inhibited when theflag is in a set state. This logic is simple and the description thereofwith reference to the drawing will be omitted.

The judgment as to whether the output of the combustion pressure sensor13 is normal or not can be made by using at least one of the combustionpressure P_(c) directly obtained from the combustion pressure sensor 13,the maximum value P_(max) of the combustion pressure P_(c) and the meaneffective pressure P_(i).

FIG. 11 is a diagram showing the engine control apparatus according toanother embodiment of the present invention.

In this embodiment, a throttle valve 3 for adjusting the inflow of airis provided in an air-intake passage 22 of an engine 21. An air-flowsensor 2 for detecting the inflow of air is provided in an upstream sideof the air-intake passage 22. An injector 26 for injecting fuel toward acombustion chamber 5 is connected to the air-intake passage 22. Anair-fuel ratio sensor (O₂ sensor) 28 for detecting the oxygenconcentration of exhaust gas to generate a detection signal whichchanges widely by reference to a theoretical air-fuel ratio is providedin an exhaust passage 8 of the engine 21. A water temperature sensor 6is provided in a tank 29 filled with water for cooling the engine. Anignition plug 11 for igniting a mixed gas in the combustion chamber 5 isprovided in a cylinder head 31 of the engine 21. A cylinder internalpressure sensor 13 for detecting pressure in the combustion chamber 5 isfurther provided in the cylinder head 31. The ignition plug 11 iselectrically connected to an ignition coil 17 through a distributor 18which is provided with a rotation sensor 16 for detecting the rotationof the engine.

The injector 26 and the ignition coil 17 are controlled by a controlunit 15. The control unit 15 receives various detection signals from theair-flow sensor 2, the cylinder internal pressure sensor 13, therotation sensor 16 and the air-fuel ratio sensor 28. As shown in FIG.12, the control unit 15 is composed of a CPU 100, an A/D converter 101for converting various analog input signals into digital signals and forsupplying those digital signals to the CPU 100, an input ROM 103 forstoring in advance the procedure for controlling the CPU 100, an RAM 104for use in the arithmetic process of the CPU 100, and output circuits105 and 106 for supplying control signals to the injector 6 and theignition coil 17 respectively.

FIG. 13 is a graph of combustion pressure (P₀) versus Crank angle. FIG.14 is a characteristic graph showing the condition in which meaneffective pressure (P_(i)) obtained from the relationship betweencombustion pressure P₀ and crank angle is changed corresponding to thechange of ignition timing. In the present invention, a control operationis carried out so that the crank angle having the maximum value of P₁can be used as target ignition timing. In particular, in a high loadrange, the air-fuel ratio feedback control is carried out so that themaximum value of P₁ becomes highest.

The control unit 15 calculates the quantity (Q_(a)) of suction air(Q_(a)) and the engine speed (N_(e)) and judges the load on the basis ofthe value Q_(a) /N_(e). When the load is not larger than a predeterminedvalue, that is to say, when the load is in the range of P in FIG. 15,ordinary fuel injection control is carried out and, at the same time,the ignition timing feedback control based on the internal pressure ofthe cylinder is carried out to obtain the maximum value of meaneffective pressure (P_(i)) in a stationary state. On the contrary, whenthe load is larger than the predetermined value, that is to say, whenthe load is in the range of E in FIG. 15, the ignition timing feedbackcontrol based on the internal pressure of the cylinder is carried out toobtain the maximum value of P₁ in a stationary state and, at the sametime, fuel cylinder is carried out to maximize P₁.

In the following, the control operation of this embodiment is describedmore in detail with reference to the flow chart of FIG. 16. In thedrawing, symbols S₁ to S₁₃ designate various steps respectively.

At the start, the quantity of suction air (Q_(a)) is read in the stepS₁. In this step, analog signals from the air-flow sensor 2 areconverted into digital values by the A/D converter 101 so that, ifnecessary, the digital values are averaged as the quantity of suctionair (Q_(a)).

Then, the engine speed (N_(e)) is read in the step S₂. In this step,N_(e) is obtained by reading and measuring the interval of the pulsesignals of the rotation sensor 16.

Then, the quantity of air per engine revolution (Q_(a) /N_(e)) iscalculated corresponding to the quantity of load of the engine in thestep S₃.

Then, in the step S₄, the output signal of the cylinder internalpressure sensor 13 is read whenever a crank angle signal is generatedfrom the rotation sensor 16. In the step S₅, mean effective pressure(P_(i)) is calculated based on the values of the output signals of thecylinder internal pressure sensor 13.

Then, in the step S₆, the judgment of load is carried out by judgingwhether the value of Q_(a) /N_(e) is larger than a predetermined valueα₁ or not.

If Q_(a) /N_(e) is not larger than α₁, the judgment proves that the loadis in the partial load range so that the step is shifted from S₆ to S₇.In the step S₇, the air-fuel ratio feedback control (O₂ feedbackcontrol) is carried out based on the output signal of the air-fuel ratiosensor 28.

Then, in the step S₈, a judgment is carried out as to whether the O₂feedback control is in operation or not. If the answer is "YES", thestep is shifted to S₉. In the step S₉, a judgment is carried out as towhether the load is in a stationary state or not. The judgment as towhether the O₂ feedback control is in operation or not is based on thejudgment as to whether various conditions, such as water temperatureconditions and air-fuel ratio sensor (O₂ sensor) activating conditions,are satisfied or not. In general, the conditions of the judgment areused in ordinary fuel injection control. On the other hand, the judgmentof stationary state is based on the judgment as to whether the absolutevalue of the deviation of Q_(a) /N_(e) per unit time is less than apredetermined value or not (Q_(a) /N_(e) may be replaced by Q_(a)). Inother words, the judgment of stationary state is based on the judgmentas to whether road conditions and the quantity of displacement of theaccelerator are constant or not.

If the judgment proves that the driving condition is in a stationarystate in the step S₉, ignition timing is controlled to maximize P_(i).The ignition timing control is carried out within a variable rangebetween a lower limit A₁ and an upper limit B₁.

If the judgment proves that the O₂ feedback control is not in operationin the step S₈ or if the judgment proves that the driving condition isnot in a stationary state in the step S₉, the step is returned to theinitial step S₁.

Then, if the relation Q_(a) /N_(e) >α₁ is satisfied in the step S₆, thatis to say, if the load is in a high load range, the step is shifted tothe step S₁₁ to judgment whether the driving condition is in astationary state or not. The judgment in the step S₁₁ is the same as thejudgment in the step S₉.

Then, if the judgment proves that the driving condition is in astationary state in the step S₁₁, the step is shifted to S₁₂. In thestep S₁₂, ignition timing is controlled to maximize P_(i). In this case,the ignition timing control is carried out within a variable rangebetween a lower limit A₂ and an upper limit B₂. Although the air-fuelratio feedback control is carried out in the partial load range, thechange of air-fuel ratio is large in the high load range. Accordingly,the variable range of ignition timing in the high load range is lessthan the variable range of ignition timing in the partial load range.For example, the variable range of ignition timing in the high loadrange is from -5° _(CA) (A₂) to +5° _(CA) (B₂) and the variable range ofignition timing in the partial load range is from -10° _(CA) (A₁) to+10° _(CA) (B₁).

Then, the step is shifted to S₁₃ to control the quantity of fuel tomaximize P_(i). The fuel control is carried out within a variable rangebetween a lower limit A₃ and an upper limit B₃.

Although the aforementioned embodiment has shown the case where thefeedback control is carried out based on mean effective pressurecalculated, as a value corresponding to the torque of the engine, fromdetection values of internal pressure of the cylinder, the invention isapplicable to the case where the feedback control of the ignition timingand the air-fuel ratio may be carried out by using as a standardparameter the crank angle at which the internal pressure of the cylindertakes a peak value, to obtain highest torque.

Although the aforementioned embodiment has shown the case where theair-fuel ratio is controlled by controlling the quantity of fuelinjection, the means for controlling air-fuel ratio is not limited tothe fuel injection controlling method.

The present invention is realized in the form of other embodiments.

As described above, according to the first invention, ignition controlis carried out based on the fuel supply quantity Q_(f) or the ignitiontiming θ_(i) to maximize at least one of the maximum pressure P_(max),the mean effective pressure P_(i) and the evaluation parameters A and Bfor every combustion cycle. Further, according to the second invention,feedback control of the fuel supply quantity Q_(f) is carried out tomake the air-fuel ratio be a predetermined value and, at the same time,the ignition timing θ_(i) is corrected to maximize at least one of themaximum pressure P_(max), the mean effective pressure P_(i) and theevaluation parameters A and B. Further, according to the thirdinvention, feedback control of the fuel supply quantity Q_(f) is carriedout to make the air-fuel ratio be a predetermined value, while thefeedback control is stopped in a predetermined range of the engine loadand, at the same time, the fuel supply quantity Q_(f) or the ignitiontiming θ_(i) is corrected to maximize at least one of the maximumpressure P_(max) the mean effective pressure P_(i) and the evaluationparameters A and B. Accordingly, maximum output power and maximumefficiency can be obtained in spite of scatter in performance ofengines.

In addition, power and efficiency can be improved while interferencebetween the air-fuel ratio feedback control based on the exhaust sensorand the maximum value control based on the combustion parameter issuppressed and, at the same time, the component concentration of exhaustgas is kept in a predetermined level or less.

Further, because the present invention is configured as described above,the air-fuel ratio feedback control as well as the ignition timingfeedback control can be made in accordance with the internal pressure ofthe cylinder even in a high load range where the air-fuel ratio feedbackcontrol could not be made in the prior art. Consequently, the best inthe torque of the engine can be brought out.

What is claimed is:
 1. An internal combustion engine control apparatuscomprising:an air-flow meter for measuring a suction air quantity Qa ofan engine; a suction pipe pressure sensor for detecting suction pipepressure P_(b) of said engine; a crank angle sensor for detecting therevolution angle θ of said engine; at least one cylinder internalpressure sensor for detecting combustion chamber pressure P_(c) of saidengine; and a control unit which comprises; means for obtaining a fuelsupply quantity Q_(f) and an ignition timing θi from an engine speed Nand one of said suction air quantity Qa and said suction pipe pressureP_(b) ; means for obtaining at least one of maximum pressure valueP_(max), a mean effective pressure P_(i), a first evaluation parameterA=P_(i) (Qa/N) and a second evaluation parameter B=P_(i) /P_(b), saidmaximum pressure P_(max) and said means effective pressure P_(i) beingcalculated from said combustion chamber pressure and said revolutionangle θ_(c) for every combustion cycle, said first evaluation parameterA being calculated from said suction air quantity Q_(a), said enginespeed N and said mean effective pressure P_(i), said second evaluationparameter B being calculated from said suction pipe pressure P_(b) andsaid mean effective pressure P_(i) ; and means for correcting at leastone of said fuel supply quantity θ_(f) and said ignition timing θ_(i) tomaximize said at least one of said maximum pressure value P_(max), saidmean effective pressure P_(i), and said first and second evaluationparameters A and B; means for controlling one of a fuel supply quantityand an ignition timing on the basis of a corrected value obtaining fromsaid correcting means; and an exhaust sensor for detecting the componentconcentration of a combustion gas, wherein said control unit furthercomprises means for obtaining an air-fuel ratio based on the componentconcentration of the combustion gas detected by said exhaust sensor, andmeans for performing a feedback control of said fuel supply quantityθ_(f) to set said air-fuel ratio to a predetermined value, saidcorrecting means corrects said ignition timing θ_(i) to maximize said atleast one of said maximum pressure value P_(max), said mean effectivepressure P_(i), and said first and second evaluation parameters A and B;and wherein in a predetermined load-operation range of said engine, saidfeedback control and the correlation of said ignition timing θ_(i) areexecuted whereas out of said load-operation range of said engine, saidfeedback control is stopped and said ignition timing θ_(i) is correctedto maximize at least one of said maximum pressure P_(max), said meaneffective pressure P_(i) and said first and second evaluation parametersA and B.
 2. An engine control apparatus comprising:air-fuel ratiocontrol means for controlling an air-fuel ratio of an engine; ignitiontiming control means for controlling the ignition timing of said engine;air-fuel ratio detection means for detecting the air-fuel ratio of saidengine; load detection means for detecting the load of said engine;cylinder internal pressure detection means for detecting the internalpressure of at least one cylinder of said engine; first feedback controlsignal generation means responsive to the output of said cylinderinternal pressure detection means for outputting a first feedbackcontrol signal to said ignition timing control means to substantiallymaximize the output torque of said engine on the basis of the cylinderinternal pressure detected by said cylinder internal pressure detectionmeans; load judgment means responsive to the output of said loaddetection means for judging whether the load of said engine is in a lowor partial load range or in a high load range. air-fuel ratio feedbackcontrol signal generation means for outputting an air-fuel ratiofeedback control signal to said air-fuel ratio control means to convergethe air-fuel ratio detected by said air-fuel ratio detection means to atheoretical value when said load judgment means judges that the load ofsaid engine is in said low or partial load range; and second feedbackcontrol signal generation means responsive to the output of saidcylinder internal pressure detection means for outputting a secondfeedback control signal to said air-fuel ratio control means tosubstantially maximize the torque of said engine when said load judgmentmeans judges that the load of said engine is in said high load range.